Roundworms in Dogs: Causes, Signs and Treatment Options

Roundworms are common intestinal parasites in dogs, especially puppies. Studies show that most puppies are born infected, and at least 30% of dogs under 6 months old have roundworm eggs in their feces.¹ Understanding roundworms in dogs can help you keep your pup healthy and prevent the spread of parasites to other dogs or people.

What Are Roundworms?

Roundworms are intestinal parasites, which means they live in a dog’s digestive tract and feed on the nutrients the dog eats. As parasites go, they are relatively large, resembling long, thin strands of spaghetti. You may see the worms in your dog’s stool or vomit after they receive a routine dose of dewormer, or in dogs with a heavy infestation. 

Harboring a large worm burden can impact growth, energy levels and overall health in young dogs. Roundworms can also infect adult dogs, but they typically cause only mild symptoms.

Types

Three main roundworm species affect dogs in North America:

• Baylisascaris procyonis (i.e., raccoon roundworm)
• Toxocara canis
• Toxascaris leonina

T. canis is most common because it is easily passed from mother dogs to their offspring before birth or during nursing, while T. leonina is not.¹

The raccoon roundworm can infect dogs or people. In dogs, infection may cause only mild symptoms. However, in people, it can cause serious neurologic disease as larvae move through the central nervous system.

How Do Dogs Get Roundworms?

Dogs can get roundworms in several different ways, which explains why the parasite is so common.

• Hunting or eating prey. Small animals, such as rodents or birds, can have roundworm larvae in their bodies. Dogs that catch or eat infected prey can then become infected themselves.
• In utero transmission. Roundworm larvae can “encyst” or become dormant in a dog’s muscles or organs. When a female dog becomes pregnant, the larvae activate and infect the puppies before birth. They can also infect puppies through the mother’s milk.
• Ingesting eggs. Infected dogs pass roundworm eggs in their feces, contaminating the environment. After a few weeks, the eggs mature and can infect another dog. When a dog sniffs, licks or eats contaminated dirt or another dog’s feces, they can become infected.

Roundworms in dogs are considered zoonotic, which means they can spread from animals to humans. People — usually children — may accidentally ingest roundworm eggs from contaminated soil, which can lead to potentially serious health problems as larvae migrate through sensitive body tissues.

Signs Your Dog May Have Roundworms

Roundworms affect dogs in different ways, depending on their age and how many worms are present. Puppies usually show the most obvious signs, while adult dogs may have only a few worms and no symptoms. Dogs can spread roundworms to others, whether they have symptoms or not.

Roundworms in dogs may cause:

• A pot-bellied appearance in puppies
• Digestive problems, such as diarrhea or vomiting
• Slow growth or dull coat in puppies
• Sudden death in very young puppies
• Visible worms in the vomit or feces

Signs of roundworm infection can be easily confused with those of other diseases. You should always check with your veterinarian if you suspect a problem with your dog’s health.

Diagnosing Roundworms in Dogs

Your veterinarian can diagnose roundworms by checking a stool sample. There are several different tests your vet may perform on a stool sample to check for parasites, including:

• Centrifugal flotation. A small amount of stool is mixed with a special solution and spun in a centrifuge so parasite eggs float to the surface. The top layer of the solution is then examined under a microscope. 
• Direct observation. Sometimes adult worms are visible in a dog’s stool or vomit. The worms are long, white and spaghetti-like in appearance.
• Polymerase chain reaction (PCR) testing. PCR testing checks for parasite DNA rather than eggs. This method is more sensitive but may cost more than a flotation test and must be performed by an outside lab.

Roundworms and other intestinal parasites may shed eggs intermittently, so a negative stool test doesn’t mean your pup is parasite-free. The Companion Animal Parasite Council recommends checking a stool sample in puppies four times during their first year, then checking twice annually in adults.¹

Diagnoses cost

The average cost* of a fecal exam to detect worms is $56, with a range of $43 to $107. Factors that may impact the cost include the size and weight of your dog, where the text is conducted and how often the test is conducted.²

Treatment Options for Roundworm

Veterinarians treat roundworms with anthelmintic medications, also called dewormers. These drugs are very safe and effective in reducing or eliminating roundworms, and they are frequently incorporated into monthly heartworm preventives to help control worms year-round.

Dewormers kill adult roundworms living in the intestines, but they don’t eliminate larvae. Your veterinarian may recommend repeating the treatment every few weeks until all life stages of the roundworm are cleared. Puppies are automatically treated with dewormers every few weeks as part of a preventive care plan, since they are assumed to have roundworms until proven otherwise.

What to expect after treatment

You may see worms passed in the stool after a deworming treatment. Although it can be alarming and unpleasant to see, dead worms mean the medicine is working. Your dog may also need a follow-up fecal exam to ensure the infection is fully resolved.

Treatment costs

The national average cost* of a deworming treatment is $34, with a range of $26 to $63.² Your dog may need more than one treatment, or more or less medication, depending on their size.

The average cost* of heartworm prevention containing an anthelmintic medication is $16 per month, but may range from $13 to $31 per month.² 

Treating the environment

Roundworm eggs can survive in harsh environments, so it’s important to clean up dog waste promptly and avoid letting dogs roam in areas that may be contaminated. Disinfecting outdoor areas may be difficult, so prevention and regular deworming are the best defenses.

Tips to Prevent Roundworm Infections

Preventing roundworms is much easier than treating repeated infections. A few consistent habits can go a long way in protecting both dogs and people.

• Administer monthly parasite preventives to adults.
• Bring a stool sample to your vet for testing at least twice a year. 
• Deworm puppies every few weeks according to your veterinarian’s prescribed schedule.
• Don’t let your dog ingest wild animals.
• Pick up and dispose of your dog’s waste promptly.
• Schedule routine veterinary exams.
• Walk your dog on a leash and discourage contact with feces left by other dogs or wild animals.

A Well-Rounded Plan

Roundworms are common parasites of puppies and adult dogs, but you can protect your pup with routine deworming, fecal checks and parasite prevention medications. Keeping your dog parasite-free not only improves their health, but also the health of other dogs and people around them.

Frequently Asked Questions About Roundworms in Dogs

Still have questions about roundworms in dogs? Here are the answers to questions pet owners frequently ask.

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Author Bio

Angela Beal, D.V.M., has more than 20 years of experience as a veterinarian. Leveraging her background in private practice and academia, she uses her passion for writing to convey information to pet owners to help them keep their pets healthy and happy.